1. Field of the Invention
This invention relates to fuel cell systems that include fuel cells and rechargeable batteries for various power needs.
2. Background Information
Many electrically powered devices, including commercial and military applications require a reliable battery with high-energy density and long life. There are numerous conventional techniques and components for charging rechargeable batteries such as lithium ion batteries which are widely used in both consumer and military electronic applications. Typically an A/C wall outlet or a 12 volt DC source commonly provided in vehicles can be used for a power source for such recharging. However, such power sources may not be available and a portable recharging device is required.
Use of a fuel cell in the power source for use as a battery recharger for a battery which is powering a portable device has been described in commonly owned U.S. Pat. No. 6,590,370, of Leach, for a SWITCHING DC-DC POWER CONVERTER AND BATTERY CHARGER FOR USE WITH DIRECT OXIDATION FUEL CELL POWER SOURCE, which issued on Jul. 8, 2003, which is currently herein incorporated by reference in its entirety.
Many commonly used battery power packs include two isolated batteries which can be connected in different ways depending on the user's needs. For example, most portable battery poweredelectronic equipment runs on either a 10-15 volt (V) low-voltage rail or a 20-30V high voltage rail. Rather than requiring two different battery types to be carried, a power pack will include two isolated 10-15V batteries with a plus and minus of each battery terminal being available on a multi-pin output connector. The user thus has the option of connecting the batteries in parallel, series, or leaving them independent to meet the power needs of the equipment.
Primary batteries are normally used where continuous, reliable operation is highly desireable because of their higher energy density and longer life as compared to rechargeable batteries. Users would prefer to commence with a fully charged battery because existing primary batteries do not have an indicator showing the amount of charge left. For this reason, many batteries are thrown away with useful life left in them. Rechargeable batteries would thus be encouraged; however, a person can not be assured that they would remain charged and would be ready at all times. A power pack that uses a fuel cell to continuously recharge the batteries so that they act essentially as primary batteries would be desired.
Batteries typically include battery protection circuits, which include switches which are used to protect the battery from under or over voltage conditions or excessive charge or discharge currents. A battery normally is packaged with it's protection circuit attached and two wires coming out of the package. To achieve all of the functionality desired of a fuel cell battery hybrid power pack, such as disconnecting the load while continuing to recharge the battery with the fuel cell power, or bypassing the battery to charge an external battery connected to the load pins, additional switches are required. However, the switches have an on resistance that results in power loss while current is flowing through the switch. It would be advantageous to have a switch network that both protects the battery and minimizes the number of switches, and therefore the total resistance, of all the current paths in the system.
It is thus object of the present invention to provide a power pack that uses one or more fuel cells as a primary energy source to charge one or more isolated rechargeable batteries so that external equipment can draw power from any of the battery(ies).
It is also an object of the invention to provide a fuel cell system that uses one or more fuel cells and one or more rechargeable batteries which can also be used to charge one or more additional external batteries.
It is also noted that a fuel cell system requires power to start (for pumps, fans, etc.), after which the fuel cell output power can be used to maintain operation. Normally this start-up power comes from a battery that is part of the power pack. It is another object of the invention to provide a mechanism by which an external power source can be used to jump-start the system even if all internal batteries are discharged.
It is yet a further object of the invention to provide an improved power pack which minimizes the number of components, such as switches, that are in the powerpath between the fuel cell(s), batteries, and the load(s).